In manufacturing semiconductor devices such as VLSI, etc., the wiring technology is a very important. Wiring is also important in the development of devices such as transistors. Cu (copper) has less resistance than Al (aluminum) which has, to do to, been used most freQuently, and hardly generates problems such as electro-migration. From this feature, the Cu wiring has a characteristic of higher reliability than the Al wiring. Efforts have therefore been made to increase the use of Cu as a wiring material in recent years.
However, when Cu or a metal containing Cu is used as a wiring material, Cu is diffused in an interlayer insulating layer (normally composed of a silicone oxide film) and this diffused Cu causes a problem of current leakage between wires. Therefore, to prevent diffusion of Cu that is used as a wiring material, it is necessary to cover the surface of Cu wire with a metal having a high melting point such as titanium (Ti) or tungsten (W) as a barrier metal layer.
One example of a conventional wire using Cu is shown in FIG. 1. A wiring layer 6 comprising Cu was formed in an interlayer insulating layer 2 on a semiconductor substrate
1. This wiring layer 6 is buried in a wiring groove 3 that was formed in the interlayer insulating layer 2. Further, a barrier metal layer 5 was formed by a metal film having a high melting point, such as TiN, between the wiring layer 6 and the interlayer insulating layer 2. This barrier metal layer 5 is formed on the inner wall surface of the wiring groove 3 before it is buried in the wiring layer 6 after, opening the wiring groove 3. Further, in FIG. 1 the barrier metal layer was not formed on the wiring layer 6, but the diffusion of Cu can be prevented by forming a dense insulating film 8 of, for instance, SiN, etc.
On the other hand, as a result of the high integration of semiconductor devices in recent years, a distance between the wiring layer 6 and an adjacent wiring layer (not shown) has become shorter. Because of this closer spacing, a capacitance component between these wiring layers cannot be disregarded. To reduce the effect of this increased capacitance component, it becomes necessary to use an insulating film having a low dielectric constant as an interlayer insulating layer.
Here, it is known that this dielectric constant of the interlayer insulating film 2 can be reduced to, for example, 3.0-3.5 from 3.9 of an oxide film by using a silicon dioxide (SiO.sub.2) mixed with fluorine as the interlayer insulating film 2. Because of this, a process to form an oxide film containing fluorine as the interlayer insulating layer 2 was tried using a plasma-CVD process.
However, fluorine (F) contained in the interlayer insulating layer 2 has a nature that tends to react with Ti, contained particularly in the barrier metal layer 5. Therefore, the problem arises that the quality of the barrier metal layer 5 changes, its nature as a barrier against Cu deteriorates, and Cu may diffuses into the interlayer insulating layer 2.
Further, the oxide film containing F formed according to the plasma-CVD process is composed of not only combined groups of Si--O and Si--F, but also combined groups of Si--CxFy, Si--HxFy and Si--OH. Here, combined groups of Si--F, Si--CxFy, Si--HxFy and Si--OH have a lower combined energy than that of a combined group of Si--O. Therefore, if an energy by heat treatment is added, --F, --CxFy, --HxFy and --OH are easily disassociated from Si-radical and react with the barrier metal layer 5. As a result, the problem arises that the nature of the barrier metal layer 5 as a barrier for wiring layer materials is deteriorated as described above.
Further, as a material for an interlayer insulating layer having a low dielectric constant, it is possible to use organic materials for insulating film using, for example, SOG (Spin-On-Glass), etc. However, as in the case when silicon oxide containing fluorine described above is used as a material for the interlayer insulating layer, this insulating membrane reacts easily with a metal comprising the barrier metal layer 5, for instance, Ti, and therefore the problem arises that Cu is diffused in the interlayer insulating layer 2.
In addition, there is a possibility that C(carbon) may mix in the interlayer insulating layer 2 from raw material gas and the interlayor insulating layer 2 may have a combined radical containing C during the manufacturing process to form wirings. As a result, the problem arises that the nature of the barrier metal layer 5 as a barrier may be deteriorated because this combined radical containing C easily reacts with a metal comprising the barrier metal layer 5 in the same manner as the combined radical containing fluorine described above.
Thus, when an insulating material having a low dielectric constant is used as an interlayer insulating layer and a metal containing Cu made with the conventional manufacturing process is used as a wire structure, there was a problem that the barrier metal layer for preventing diffusion of Cu into the interlayer insulating layer reacted with the interlayer insulating layer material, and the nature of the barrier metal layer was deteriorated.